As an aluminum heat exchanger, one comprised of the material forming the aluminum working fluid passages to which the material forming the aluminum alloy fins are brazed has been used. To improve the performance and characteristics of heat exchangers, this aluminum alloy fin material is required to have a sacrificial anodic effect to prevent corrosion of the material forming the working fluid passage and required to have excellent sag resistance and erosion resistance so that the fin material does not deform and the brazing material does not penetrate into the fin material due to high temperature heating at the time of brazing.
The fin material has Mn, Fe, Si, Zn, etc. added to it to satisfy the above basic properties, but recently, the production process has been improved to develop high strength aluminum alloy fins for heat exchanger use with a low tensile strength before brazing and a high tensile strength after brazing and heat conductivity.
PLT 1 discloses a method of production of an aluminum alloy fin material for brazing use which satisfies the above properties required for fin materials and provides a fin material which can be made thinner by casting an aluminum alloy melt which has a specific composition to an aluminum alloy sheet by a twin roll type continuous casting and rolling method, cold rolling it, and annealing it two times or more by intermediate annealing.
The fin material which is proposed in PLT 1 raises the braze dispersion resistance by holding the rolled structure (fibrous structure) until brazing heating. However, a fin material which is reduced in thickness tends to become larger in springback. When made corrugated, there was the concern that a predetermined fin pitch could no longer be obtained.
PLT 2 discloses an aluminum alloy fin material which contains Si: 0.7 to 1.3 wt %, Fe: over 2.0 wt % to 2.8 wt %, Mn: over 0.6 wt % to 1.2 wt %, and Zn: over 0.02 wt % to 1.5 wt %, has a balance of Al and unavoidable impurities, has 110,000/mm2 or more intermetallic compounds with maximum sizes of 0.1 to 1.0 μm, and has a grain size after brazing of 150 μm or more.
The fin material which is described in PLT 2 has an electrical conductivity after brazing of 50% IACS or more and an excellent heat conductivity, but even if Fe is over 2.0 wt % to 2.8 wt % and the solidification cooling speed is relatively fast as with a twin belt casting machine, coarse Al—(Fe.Mn)—Si-based precipitates are formed at the time of casting and production of a sheet material is liable to become difficult.
PLT 3 discloses a method of production of an aluminum alloy fin material for brazing use which satisfies the above properties required for fin materials and provides a fin material which can be made thinner by casting an aluminum alloy melt which has a specific composition to an aluminum alloy slab by a twin belt type continuous casting method, cold rolling it, and annealing it by intermediate annealing.
Further, the fin material for a heat exchanger is formed into a predetermined shape by corrugation etc. before brazing the fin material with other members of the heat exchanger. At this time, the high hardness second phase particles which are present in the metal structure of the fin material promote the abrasion of the shaping mold and the lifetime of the mold become shorter.
PLT 4 discloses the art in which the number of 1 μm or more second phase particles per unit area present in the metal structure of the fin material is defined so as to improve the mold wear characteristic.
However, if trying to further reduce the thickness of a fin material and raise the tensile strength of a fin material, there has been the concern for springback easily occurring at the time of corrugation and the formability falling like in the past.